Long-term substitute teacher Kim Herdell, left, explains the concepts of exponents to student Xoe Cesarini, 16, right, during an Algebra 1 class Monday at Anclote High School in Holiday. Herdell says she substitutes exclusively at Anclote High because she feels welcome.

She worked for other schools closer to her home when her daughter first entered elementary school six years ago. But Herdell didn't feel welcomed.

"I never saw any administrator approach me or anyone who subbed to even introduce themselves or say 'Nice to have you here,' " she recalled. "You literally were just kind of like a shadow. You weren't acknowledged."

All that changed when Herdell arrived at Anclote High, where she said the administration and staff value her as a member of their team. She now subs only at Anclote, often taking longer-term spots and refusing requests from any other campus.

"I have never felt like a sub at this school," she said.

Herdell's experience is not unique. District officials have heard complaints from substitutes about their poor treatment and seen the subsequent results.

Many schools struggle to fill their daily substitute teaching needs, superintendent Kurt Browning recently told the Pasco School Board. Some have seen their daily unfilled rate surpass 30 percent.

On the day after the Martin Luther King Jr. holiday, schools districtwide called for about 400 substitute teachers. Only about 250 responded.

When that happens, the schools still have to ensure every classroom is covered during every period. That means asking faculty members to volunteer their lunch or planning periods, or taking qualified staff away from their regular assignments.

Perceived poor treatment at some schools, low pay and school location all contribute to the lack of substitute teachers.

"We have enough subs, in theory, to cover all the absences," assistant superintendent Ray Gadd said. "They're just not answering their phones."

Administrators are exploring solutions.

Browning said he intended to bring a new pay structure to the board during budget preparations. Currently, Pasco subs earn $55 to $75 a day, depending on their education and experience. By contrast, Pinellas subs can make up to $130 a day if they work at high priority schools.

Hillsborough County, which has averaged 27 percent of its substitute positions going unfilled, pays similarly to Pasco.

The Pasco human resources department also is exploring whether to contract out substitute management, and seeking a fix to a computer glitch that doesn't immediately remove subs from the available list once they accept a position. The latter problem can leave schools in the lurch when a sub takes a spot and then switches to another closer to home.

The treatment of subs is critical, Browning also noted. He suggested calling them "guest teachers" as one small way to convey added respect.

Herdell didn't see a name change as a necessary move. Neither did some of the students she has worked with over the years.

"They are what they are — subs," said Anclote High senior Anthony Padilla. "Guest teacher, sub teacher, it's the same thing."

If substitute teachers want respect, he said, they can earn it by not acting like babysitters.

Both students said Herdell has helped them with their class work and is visible in the hallways interacting with the kids.

"You can depend on her when you need something," Tlanepantla said.

"You can tell she really cares about her students," Padilla added. "I don't think you really get that from subs."

Still, as in any classroom, student behavior can pose a challenge, and on a recent school day Herdell struggled to explain a math lesson as kids fiddled with their phones and talked. Herdell said that some classes aren't easy, but she chose to focus on the positives.

"Just because you might have gotten a rough group of kids one day, you could get a whole different group the next day. It might have just been a bad day," she said. "Everybody has them."

Anclote High principal Michelle Williams acknowledged that not everyone wants to put up with the bad days. And it can be difficult to find people who are a good fit for the job, she added.

The troubles grow as a school uses its most reliable subs for longer-term spots, such as replacing teachers on personal leave, she said, shrinking the pool of regulars available for short-term needs.

That's why treating the subs right is important.

At Smith Middle, which had a 34 percent unfilled rate in 2012-13, a planning team took this issue to heart. In addition to offering extra classroom assistance and including subs in school activities, the leadership did start calling subs "guest teachers."

They also decided to count any positive behavior rewards that students received from subs as worth double.

Students "know they better behave and do their best with that substitute," principal Margie Fackelman said. "We just try to treat them with respect and make them feel welcomed."

At the same time, Fackelman said, the school has reduced its need, because fewer classroom teachers are calling in sick this year than last. That means less reliance on subs, and also less asking other faculty and staff members to pick up the slack.